Reforming with multimetallic catalysts

ABSTRACT

A process for desensitizing a hypersensitive, high activity reforming catalyst for suppression of hydrogenolysis which is particularly acute during the early portion of the period that the catalyst is placed on stream, i.e., at the startup of a reactor. The catalyst is constituted of a composite which includes a Group VIII noble metal hydrogenation-dehydrogenation component, notably platinum, iridium or rhenium, and tellurium. Hydrogenolysis is suppressed by incorporating within such reforming catalyst at the time of its preparation an element, or a compound or salt of tellurium. In another of its aspects the present invention embodies a reforming catalyst or catalyst composite comprising a refractory or inorganic oxide support material, particularly alumina, a Group VIII noble metal hydrogenation-dehydrogenation component, notably platinum, to which iridium or rhenium, and tellurium have been added to promote the activity and selectivity of the catalysts, and said catalyst is prepared by a method wherein tellurium is introduced into and deposited throughout said support. Suitably, the reforming catalyst, or composite also contains a halogen component, particularly chlorine and preferably the tellurium component is introduced into the support, or catalyst, by impregnating with a solution comprising an element, salt, acid or compound of tellurium.

This is a division of application Ser. No. 862,115, filed Dec. 19, 1977, which is a continuation - in - part of application Ser. No. 826,996, filed Aug. 23, 1977 and now abandoned.

Catalytic reforming, or hydroforming, is a well-known type of process employed in the petroleum refining industry for improving the octane quality of naphthas and straight run gasolines. In a typical process, a series of reactors are provided with fixed beds of catalyst which receive upflow or downflow feed, and each reactor is provided with a heater, or interstage heater, because the reactions which take place are endothermic. A naphtha feed, with hydrogen, or recycle gas, is cocurrently passed sequentially through a reheat furnace and then to the next reactor of the series. The vapor effluent from the last reactor of the series is a gas rich in hydrogen, which usually contains small amounts of normally gaseous hydrocarbons, and it is separated from the C₅ ⁺ liquid product and recycled to the process to minimize coke production; coke invariably foaming and depositing on the catalyst during the reaction.

Reforming catalysts are recognized as dual functional, the catalyst composite including a metal, or metals, or a compound or compounds thereof, providing a hydrogenation-dehydrogenation function and an acidic component providing an isomerization function. The plantinum group or Group VIII noble metals (ruthenium, osmium, rhodium, iridium, palladium and platinum) despite their expense have been recognized as having a combination of properties which make them particularly suitable for reforming operations, and hence certain of these species of catalysts have become widely used in commercial operations. Conventional reforming catalysts have thus long employed platinum composited with an inorganic oxide base, particularly alumina, and in recent years promoters such as iridium, rhenium, germanium, tin, etc., have been added, particularly to platinum, to enhance one or more of certain of the characteristics which a good reforming catalyst must possess--viz., activity, selectivity, activity maintenance and yield stability. Halogen, e.g., chlorine, is generally added to enhance the acid function required of the catalyst.

The principal reactions produced in reforming are: (1) dehydrogenation of naphthenes to produce the corresponding aromatic hydrocarbons, e.g., methylcyclohexane is dehydrogenated to form toluene, (2) isomerization on n-paraffins to form branched-chain paraffins and isomerization of ring compounds, e.g., the isomerization of ethylcyclopentane to form methylcyclohexane, and dehydrogenation of the latter to form toluene, (3) dehydrocyclization of paraffins to form aromatics, e.g., the dehydrocyclization of n-heptane to form toluene, and (4) hydrocracking of high molecular weight feed constituents to form lower molecular weight, or lower boiling, constituents, e.g., the cracking of n-decane to produce C₃ and C₇ hydrocarbons. The net effect of these reactions is to increase the concentration of aromatics and isomers, with consequent octane improvement of naphthas boiling within the gasoline range.

Hydrogenolysis, a specific and severe form of hydrocracking which produces methane can also occur, and is particularly acute in reforming with the new "multi-metallic" catalysts, e.g., platinum-rhenium, platinum-iridium, etc., particularly fresh or regenerated, reactivated catalysts of such type, which are particularly hypersensitive. Exotherms or heat fronts are produced which pass through a catalyst bed at startup, i.e., when new or freshly regenerated, reactivated catalyst is initially contacted with hydrocarbons at reforming temperatures. The temperature excursions or heat fronts are attributed to the hyperactivity of the catalyst which causes excessive hydrocracking of the hydrocarbons, or hydrogenolysis, sometimes referred to as "runaway hydrocracking." These temperature excursions or heat fronts are undesirable because the resultant temperature often results in damage to the catalyst, or causes excessive coke laydown on the catalyst with consequent catalyst deactivation and, if uncontrolled, may even lead to damage to the reactor and reactor internals. The phenomenon is troublesome in any type of reforming operation, but is particularly troublesome in cyclic reforming wherein one reactor of the series is a swing reactor which is used as a substitute for each of the other reactors so that the catalyst of each in turn can be regenerated, and reactivated. Because of the frequency with which the catalysts must be regenerated in cyclic reforming, as contrasted with other type of reforming units, hydrogenolysis, or runaway hydrocracking greatly reduces the efficiency of the cyclic reforming process and simply cannot be tolerated. In fact, because of this problem some of the newer more highly active promoted platinum catalysts, i.e., multimetallic catalysts, are unsuitable in cyclic reforming processes.

It is conventional to presulfide a noble metal reforming catalyst prior to its use in reforming to suppress hydrogenolysis, or runaway hydrocracking, which can cause excessive methane formation, hot spots, temperature excursions, and the like. In presulfiding, it is conventional to charge catalyst into a reactor for contact with an admixture of hydrogen sulfide and an inert gas, e.g., nitrogen. Various difficulties, however, are associated with this practice. One difficulty of such technique, e.g., is that the sulfur is not deposited uniformly on the catalyst. The catalyst at the top of the reactor is heavily sulfided and only lightly sulfided near the bottom of the reactor. Only by sulfiding to the point of breakthrough can the catalyst at the bottom of the reactor be adequately sulfided, this causing the catalyst on the top of the reactor to be over-sulfided. Whereas this non-uniformity and over-sulfiding of the catalyst does not create particularly difficult problems in the use of unpromoted platinum catalysts, it produces particularly acute problems with the new multimetallic catalyst species. Excess sulfur is converted into hydrogen sulfide which is picked up by the recycle gas such that it contaminates the entering feed. This, because of the high sulfur sensitivity of these catalysts, results in more rapid catalyst deactivation and loss of C₅ ⁺ liquid yields. Moreover, during regeneration, some of the sulfur is oxidized to sulfur dioxide and sulfur trioxide which forms corrosive acids with water introduced into the process and contributes to sulfation of the inorganic oxide or alumina base, resulting in loss of surface area and activity.

Another problem is that the new, fresh, or regenerated multimetallic catalysts, especially iridium-containing catalysts, and notably platinum-iridium catalysts, become rapidly overheated when exposed, in the presence of hydrogen, at normal reaction conditions to hydrocarbons, which can crack to produce methane, ethane, propane and butane, to such extent that the catalyst itself can be overheated, sintered or otherwise damaged.

In U.S. Pat. No. 3,884,799 to Mahoney et al, which issued May 20, 1975, there is disclosed a catalyst, and process for using such catalyst for reforming a petroleum hydrocarbon fraction at conventional reforming conditions, which is constituted of a Group VIII noble metal, notably platinum, and rhenium and selenium composited on a refractory inorganic oxide, notably alumina, to which is added a halogen component, notably a chloride. This reference discusses the problem of hydrogenolysis which occurs in reforming during start-up with an unsulfided, or improperly sulfided, halogenated platinum-rhenium catalyst, and it discloses and claims the process of using a catalyst in reforming in which selenium is incorporated therein thereby reducing coke formation and eliminating any necessity of a pre-sulfiding treatment of that particular catalyst to suppress hydrogenolysis during start-up. Moreover, it is suggested that an substantial amount of the selenium is retained on the catalyst during reforming, and subsequently after the catalyst has been subjected to an appreciable number of simulated regeneration cycles. This provides advantages in that the catalyst need not be retreated after each regeneration regeneration presulfiding of the catalyst becomes unnecessary. U.S. Pat. No. 2,851,399 to Brennan et al also discloses a reforming catalyst containing platinum and selenium composited with alumina useful in reforming but, inter alia, there is no suggestion of a third hydrogenation-dehydrogenation component.

It is accordingly a primary objective of the present invention to obviate these and other prior art deficiencies and, in particular, to provide the art with a new and improved startup process for upgrading naphthas by reforming with iridium or rhenium containing catalysts to produce higher octane gasolines.

A further object is to provide a new and improved cyclic reforming process for effecting, at suitable reforming conditions, the production of high octane gasolines while minimizing hydrogenolysis, particularly runaway hydrocracking, especially when employing iridium-, or rhenium-containing catalysts, notably platinum-iridium catalysts.

These and other objects are achieved in accordance with the present invention embodying a process comprising incorporating tellurium, or a compound or salt of tellurium, within an iridium-, or rhenium-containing reforming catalyst, notably a platinum-iridium catalyst, at the time of its preparation. Tellurium is identified as a Group VIA element (Periodic Table of the Elements; Sargent-Welch Scientific Company, Copyright 1968) having an atomic number of 52 and an atomic weight of 127.6. Exemplary of suitable tellurium compounds and salts for this purpose are tellurium dibromide, tellurium hexafluoride, tellurium methoxide, tellurium sulfur oxide, tellurous acid, telluric acid, and the like.

In another of its aspects the present invention embodies a reforming catalyst or catalyst composite comprising a refractory or inorganic oxide support material, particularly alumina, a Group VIII noble metal hydrogenation-dehydrogenation component, notably platinum, to which iridium, or rhenium, or both, and tellurium have been added to promote the activity and selectivity of the catalysts, and said catalyst has been prepared by a method wherein the tellurium is introduced into and deposited throughout said support. Suitably, the reforming catalyst, or composite also contains a halogen component, particularly chlorine, and preferably the tellurium component is introduced into the support, or catalyst, by impregnating same with a solution comprising tellurium as an element, or a salt or compound thereof. Alternatively, the tellurium can be deposited on the support by sublimation of a volatile tellurium compound such as tellurium dioxide.

The incorporation of tellurium into the catalyst at the time of its formation, though the reasons therefor are not as yet completely understood, obviates any need for in situ sulfiding of the catalyst with H₂ S as in conventional practice. The tellurium remains within the catalyst throughout the operation suppressing hydrogenolysis, and yet does not create the problems associated with conventional catalyst sulfiding. The presence of tellurium within the catalyst not only suppresses hydrogenolysis but additionally enhances the reforming characteristics of the catalyst.

In accordance with this invention, a porous refractory inorganic oxide support is employed as a suitable impregnation material. The support can contain, for example, one or more of alumina, bentonite, clay, diatomaceous earth, zeolite, silica, activated carbon, magnesia, zirconia, thoria, and the like; though the most preferred support is alumina to which, if desired, can be added a suitable amount of other refractory carrier materials such as silica, zirconia, magnesia, titania, etc., usually in a range of about 1 to 20 percent, based on the weight of the support. A preferred support for the practice of the present invention is one having a surface area of more than 50 m² /g., preferably from about 100 to about 300 m² /g., a bulk density of about 0.3 to 1.0 g/ml, preferably about 0.4 to 0.8 g/ml, an average pore volume of about 0.2 to 1.1 ml/g., preferably about 0.3 to 0.8 ml/g., and an average pore diameter of about 30 to 300 A.

The metallic component of the Group VIII noble metals of the Periodic Table of the Elements necessarily includes iridium or rhenium, or both, and one or more platinum group metal components such as ruthenium, rhodium, palladium, osmium, platinum, and the like. Of these latter class of metals, platinum is the preferred component, and platinum-iridium catalyst, the preferred species of catalysts which can be further promoted to increase the normally expected activity and selectivity of these catalysts.

The additional metallic component, or components, is suitably a component selected from the Group IV (Ge, Sn, Pb) metals, Group VI (Cr, Mo, W) metals, Group VII metals, and Group VIII metals. For example, germanium, tin, lead, osmium, ruthenium, or rhodium can be used. Although one or more of these components can be added by any of the conventional methods, it is preferably to add them by an impregnation prior to, following or simultaneously with the impregnation of the Group VIII noble metal, iridium or rhenium (or both), tellurium or halogen components. The tellurium and other promoter metals are added in concentration ranging about 0.01 to 3 percent, preferably from about 0.03 to about 1 percent, based on the weight of the catalyst.

The metal hydrogenation components can be composited or intimately associated with the porous inorganic oxide support or carrier by various techniques known to the art such as ion-exchange, coprecipitation with the alumina in the sol or gel form, and the like. For example, the catalyst composite can be formed by adding together suitable reagents such as a salt of platinum and ammonium hydroxide or ammonium carbonate, and a salt of aluminum such as aluminum chloride or aluminum sulfate to form aluminum hydroxide. The aluminum hydroxide containing the salts of platinum can then be heated, dried, formed into pellets or extruded, and then calcined in nitrogen or non-agglomerating atmosphere. The metal hydrogenation components can also be added to the catalyst by impregnation, typically via an "incipient wetness" technique which requires a minimum of solution so that the total solution is absorbed, initially or after some evaporation.

It is generally peferred, however, to deposit the Group VIII noble metal, or metals, iridium and metals used as promoters, on a previously pilled, pelleted, beaded, extruded, or sieved particulate support material by the impregnation method. Pursuant to the impregnation method, porous refractory inorganic oxides in dry or solvated state are contacted, either alone or admixed, or otherwise incorporated with a metal or metals-containing solution, or solutions, and thereby impregnated by either the "incipient wetness" technique, or a technique embodying absorption from a dilute or concentrated solution, or solutions, with subsequent filtration or evaporation to effect total uptake of the metallic components.

The Group VIII noble metal component (iridium or rhenium, tellurium, and the metals used as promoters) is supported on the carrier within the range of from about 0.01 to 3 percent, preferably from about 0.05 to 1 percent, based on the weight of the catalyst. In compositing the Group VIII noble metal with the carrier, essentially any soluble compound can be used, but a soluble compound which can be easily subjected to thermal decomposition and reduction is preferred, for example, inorganic salts such as halide, nitrate, inorganic complex compounds, or organic salts such as the complex salt of acetylacetone, amine salt, and the like. Where the Group VIII noble metal is platinum, platinum chloride, platinum nitrate, chloroplatinic acid, ammonium chloroplatinate, potassium chloroplatinate, platinum polyamine, platinum acetylacetonate, and the like, are preferably used.

The impregnation solution of the noble metal compound, and metals used as promoters, are prepared by dissolving the compounds in water or any other inorganic or organic solvent. The concentration of the metallic component ranges from about 0.01 to 5 percent, preferably from about 0.05 to 1 percent, based on the weight of solution. The pH of the impregnation solution should be controlled to less than about 4, preferably less than 3, by the addition of a suitable inorganic or organic acid. By controlling the pH within these ranges, the components can be effectively dispersed into the inner part of the catalyst. Generally, it is preferred to use a halogen-acid aqueous solution of the noble metals.

In accordance with this invention, the tellurium is incorporated into the catalyst at the time of its formation and preferably tellurium is incorporated by impregnation of a solution of a soluble salt, acid or compound of tellurium into the carrier. This can be carried out simultaneously with, prior to, or following the impregnation of the hydrogenation-dehydrogenation component, or components, into the carrier. Tellurium, in accordance with this invention, can be added to the carrier from a solution which contains both the salt, acid or compound of tellurium, the Group VIII noble metal hydrogenation-dehydrogenation component, or components, iridium or rhenium, and the inorganic acid such as HCl. Suitably, the salts or compounds are dissolved in a suitable solvent, preferably water, to form a solution, or each moiety is separately dissolved in a solution, the solutions admixed and the admixed solution used for impregnation of the carrier.

The concentration of the salt or compound of tellurium in the impregnation solution ranges from about 0.01 to 2 percent, preferably from about 0.01 to 1 weight percent, based on the weight of the solvent; this concentration being adequate to impregnate generally from about 0.001 to about 3 percent, preferably from about 0.01 to about 1 percent of the tellurium within the catalyst.

The impregnation of the Group VIII noble metal, iridium or rhenium, and tellurium components into a carrier is carried out by impregnating the carrier with the solution of the respective salts or compounds of the elements or metals to be incorporated. The amount of impregnation solution used should be sufficient to completely immerse the carrier, usually within the range from about 1 to 20 times of the carrier by volume, depending on the metal concentration in the impregnation solution. The impregnation treatment can be carried out under a wide range of conditions including ambient or elevated temperatures and atmospheric or supratmospheric pressures.

In a preferred embodiment of the present invention a carrier can be impregnated with an aqueous halogen-acid solution of the Group VIII noble metal, iridium or rhenium, and other compounds, if any, followed by evaporation or filtration and then drying or calcination, or both, and then the metals impregnated catalysts can be impregnated with a solution containing a dissolved salt or compound of tellurium followed by evaporation or filtration and then drying or calcination, or both, whereby the tellurium component can be dispersed substantially uniformly to the inner part of the catalyst.

To enhance catalyst performance, it is also required to add a halogen component. Fluorine and chlorine are preferred halogen components. The halogen is contained on the catalyst within the range of 0.1 to 3 percent, preferably within the range of about 0.3 to 2 percent, based on the weight of the catalyst. When using chlorine as a halogen component, it is contained on the catalyst within the range of about 0.2 to 2 percent, preferably within the range of about 0.5 to 1.5 percent; based on the weight of the catalyst. The introduction of halogen into catalyst can be carried out by any method and at any time of the catalyst preparation, for example, prior to, following or simultaneously with the impregnation of the noble metal, iridium or rhenium, or tellurium components. In the usual operation, the halogen component is introduced simultaneously with the incorporation of the noble metal component. It can also be introduced by contacting a carrier material in a vapor phase or liquid phase with a halogen compound such as hydrogen fluoride, hydrogen chloride, ammonium chloride, or the like.

The catalyst is dried by heating at a temperature above about 80° F., preferably between about 150° F. and 300° F., in the presence of nitrogen or oxygen, or both, in an air stream or under vacuum. The catalyst is calcined at a temperature between about 500° F. to 1200° F., preferably about 500° F. to 1000° F., either in the presence of oxygen in an air stream or in the presence of an inert gas such as N₂.

The feed or charge stock can be a virgin naphtha, cracked naphtha, a Fischer-Tropsch naphtha, or the like. Typical feeds are those hydrocarbons containing from about 5 to 12 carbon atoms, or more preferably from about 6 to about 9 carbon atoms. Naphthas, or petroleum fractions boiling within the range of from about 80° F. to about 450° F., and preferably from about 125° F. to about 375° F., contain hydrocarbons of carbon numbers within these ranges. Typical fractions thus usually contain from about 20 to about 80 Vol.% paraffins, both normal and branched, which fall in the range of about C₅ to C₁₂, from about 10 to 80 Vol.% of naphthenes falling within the range of from about C₆ to C₁₂, and from 5 through 20 Vol.% of the desirable aromatics falling within the range of from about C₆ to C₁₂.

The reforming runs are initiated by adjusting the hydrogen and feed rates, and the temperature and pressure to operating conditions. The run is continued at optimum reforming conditions by adjustment of the major process variables, within the ranges described below:

    ______________________________________                                         Major Operating                                                                             Typical Process                                                                              Preferred Process                                   Variables    Conditions    Conditions                                          ______________________________________                                         Pressure, Psig                                                                              50-750        100-300                                             Reactor Temp., ° F.                                                                  750-1100       850-1000                                           Gas Rate, SCF/B                                                                              1500-10,000  2000-7000                                           (Incl. Recycle Gas)                                                            Feed Rate, W/W/Hr                                                                           0.5-10        1-3                                                 ______________________________________                                    

The invention will be more fully understood by reference to the following nonlimiting demonstrations and examples which present comparative data which illustrate its more salient features. All parts are given in terms of weight except as otherwise specified.

EXAMPLE 1

In order to demonstrate a preferred mode of practicing the present invention, certain selected salient data are set forth hereafter. In preparing for these demonstrations, a commercial platinum-iridium catalyst (Catalyst A) of the following weight percent composition was first prepared, and then dried at 300° F. and calcined at 500° F., to wit:

    ______________________________________                                         Catalyst A                                                                     ______________________________________                                         Platinum              0.3%                                                     Iridium               0.3%                                                     Chlorine              0.9%                                                     Alumina               98.5%                                                    ______________________________________                                    

A second catalyst, Catalyst B, was prepared from Catalyst A by sulfiding with H₂ S in hydrogen stream at 900° F. to incorporate 0.067 wt.% S on the catalyst. Catalyst B is thus of the following approximate composition, to wit:

    ______________________________________                                         Catalyst B                                                                     ______________________________________                                         Platinum              0.3%                                                     Iridium               0.3%                                                     Chlorine              0.9%                                                     Sulfur                0.067%                                                   Alumina               98.5%                                                    ______________________________________                                    

Catalyst C was prepared from a portion of Catalyst A by impregnating with an aqueous solution containing sufficient H₂ TeO₄ to impregnate 0.12 percent of tellurium into the catalyst. The composition of Catalyst C is as follows:

    ______________________________________                                         Catalyst C                                                                     ______________________________________                                         Platinum              0.3%                                                     Iridium               0.3%                                                     Chlorine              0.9%                                                     Tellurium             0.12%                                                    Alumina               98.4%                                                    ______________________________________                                    

The catalysts were each then contacted at reforming condition in separate runs with Karlsruhe Aramco naphtha, characterized in Table I as having the following inspections:

                  TABLE I                                                          ______________________________________                                         ASTM Distillation, ° F.                                                  Initial               151                                                      10                    191                                                      20                    208                                                      30                    224                                                      40                    239                                                      50                    255                                                      60                    270                                                      70                    289                                                      80                    310                                                      90                    334                                                      Final B.P.            361                                                     Octane No., RON Clear  40.0                                                    Gravity, ° API  60.0                                                    Sulfur, Wt. ppm        0.8                                                     Analysis, Vol. Percent                                                          Paraffins             67.4                                                     Naphthenes            19.5                                                     Aromatics             13.1                                                    ______________________________________                                    

The conditions at which the reforming runs were carried out, and the results obtained are given in Table II.

                                      TABLE II                                     __________________________________________________________________________     Results of Reforming of Karlsruhe Aramco                                       Naphtha at 910° F. 200 Psig, 3.1 W/Hr/W and 5000 SCF H.sub.2 /B         Catalyst Age: 28 Hours                                                         Method of                                                                      Incorporation, Wt. % Incorporated                                              and Substance  Substance on      Wt. % on Feed                                 Catalyst                                                                            Incorporated                                                                             Catalyst  ppm S in Feed                                                                          C.sub.1                                                                           C.sub.1 + C.sub.2 + C.sub.3 +                                                  C.sub.4    C.sub.5 +                                                                         Arom.                        __________________________________________________________________________     A    None      0.0       <0.1    52.2                                                                              83.6*      21.9*                                                                             23.7                         A    None      0.0       0.8     19.3                                                                              52.4*      48.9                                                                              40.8                         B    H.sub.2 S Treatment                                                                      0.067     0.8     4.1                                                                               24.8       73.6                                                                              50.1                              at 900° F.                                                         C    H.sub.2 TeO.sub.4 Impreg.                                                                0.12      0.8     8.2                                                                               30.0       67.0                                                                              46.1                         __________________________________________________________________________      *Negative hydrogen make                                                  

The first few hours of a reforming cycle are critical since at this stage excessive hydrogenolysis, or runaway hydrocracking can occur increasing the temperature of the bed which in turn can lead to more cracking; and this condition can result in reactor melt down. However, excessive hydrogenolysis did not occur in any of these runs which utilized Catalysts B or C. Referring specifically to Table II, it is seen that Catalyst A results in excessive light gas make (C₁, C₂, C₃ and C₄) and causes a loss in the desired C₅ ⁺ yield. This situation is particularly pronounced with the low sulfur (<0.1 ppm) feed. Catalyst B prepared by the known H₂ S treatment lowers the initial cracking and enables catalyst to be handled in a safe manner.

The beneficial effects of H₂ TeO₄ impregnation are shown by the results observed with Catalyst C. The amount of cracking obtained in the run which utilized Catalyst C is significantly less than with Catalyst A, through somewhat higher than with the conventionally H₂ S treated Catalyst B. The C₅ ⁺ yield is increased considerably. This yield increase is accompanied by an appreciable gain in aromatics content which according to known correlations results in higher octane.

The following example illustrates the advantages of incorporating tellurium within a rhenium-containing catalyst, and also exemplifies material differences which exist between tellurium and selenium for use in promoting rhenium-containing catalyst vis-a-vis iridium-containing catalysts.

EXAMPLE 2

Specifically, to illustrate the performance of rhenium-containing catalysts containing small amounts of tellurium, reforming tests were conducted with platinum-rhenium catalysts to which had been added a small amount of tellurium and selenium, respectively, and those were compared with commercially available platinum-rhenium catalysts, one of which was pretreated with hydrogen sulfide as commercially practiced and the other of which was not pretreated.

These catalysts, each of which is identified hereafter and designated as Catalysts D, E, F and G, were contacted at reforming conditions adequate to produce close to a 100 RON C₅ liquid product in separate runs with a commercially available low sulfur paraffinic naphtha, characterized in Table III as having the following inspections:

                  TABLE III                                                        ______________________________________                                         ASTM Distillation, ° F.                                                  Initial               145                                                      10                    181                                                      20                    204                                                      30                    222                                                      40                    240                                                      50                    258                                                      60                    275                                                      70                    293                                                      80                    313                                                      90                    334                                                      Final B.P.            363                                                     Octane No., RON Clear  34.8                                                    Gravity, ° API  59.7                                                    Sulfur, Wt. ppm        <0.1                                                    Analysis, Vol. Percent                                                          Paraffins             69.509                                                   Naphthenes            18.411                                                   Aromatics             12.08                                                   ______________________________________                                    

The identity of each of the catalysts which contain, besides the added sulfur, tellurium or selenium components, if any, in the amount designated also contain 0.3 wt. % platinum, 0.3 wt. % rhenium and 1 wt. % chlorine composited with alumina, dried and calcined as in the previous example. The results of runs conducted with these catalysts, at the designated conditions for an initial six hour balance period are as given in Table IV.

                                      TABLE IV                                     __________________________________________________________________________     REFORMING OF LOW SULFUR (<0.1 PPM) PARAFFINIC FEED                             at 930°, 200 PSIG 5000 SCF/B and 1.4 W/H/W                              Initial 6 Hour Balance Period                                                                                       Wt. % on Feed                                                    C.sub.5 + Yield at           Wt. Ratio Aromatics        Identify of Catalyst, and Treatment                                                                   100 RON, Volume %                                                                            CH.sub.4                                                                           C.sub.1 + C.sub.2 + C.sub.3 +                                                  C.sub.4    C.sub.1 + C.sub.2 +                                                            C.sub.3                    __________________________________________________________________________                                                         + C.sub.4                  D Standard catalyst; not pretreated                                                                   60.9          6.9 30.3       45.1                       E Presulfided with H.sub.2 S (0.06% S)                                                                67.6          2.7 24.7       50.2                       F 0.06% Te via H.sub.2 TeO.sub.4 impreg.                                                              67.7          5.9 32.3       52.1                       G 0.04% Se via H.sub.2 SeO.sub.3 impreg.                                                              53.9          25.6                                                                               58.4       36.3                       __________________________________________________________________________

These data show a profound advantage for tellurium as a promoter. Selenium, on the other hand, promotes cracking in the early part of the run and is not advantageous for platinum-rhenium catalysts. Tellurium is thus fully equivalent to the conventional sulfide treatment in C₅ + liquid yield and, though it produces more methane and light gases than a sulfided catalyst, it produces a greater yield of aromatics. It is of course, superior in all respects to the use of an untreated platinum-rhenium catalyst. Only at the end of 55 hours of operation did the platinum-rhenium-selenium catalyst operate satisfactorily without excessive methane and light gas yield, loss of aromatics, and C₅ ⁺ liquid product yield; at which time the performance approximated that of the catalyst to which tellurium had been added.

It is apparent that various modifications and changes can be made without departing the spirit and scope of the present invention, outstanding features of which are that hydrogenolysis can be suppressed without the use of conventional catalyst presulfiding techniques, and the octane quality of hydrocarbon feedstocks can be upgraded and improved. 

Having described the invention, what is claimed is:
 1. A process for reforming a hydrocarbon feed at reforming conditions which comprises contacting said feed at reforming conditions with a catalyst which comprises a Group VIII noble metal hydrogenation-dehydrogenation component, a component comprised of iridium or rhenium, or both, a halogen component, and sufficient of a tellurium component to increase the activity or selectivity, or both, as contrasted with a catalyst otherwise similar except that it does not contain tellurium.
 2. The process of claim 1 wherein the catalyst is comprised of platinum, an iridium or rhenium, and tellurium components. 